\begin{tikzpicture}
    \tkzDefPoints{0/0/O, 2/0/Q, -0.5/1.0/P}
    \tkzDefPoint(20:1.5){A}

    \tkzDrawCircle[thick](O,A)
    \tkzDrawSegments(O,A  O,P  O,Q)
    \tkzDrawPoints(O,P,Q)
    \tkzLabelSegment[above](O,A){$r$}
    \tkzLabelPoints[left](O,P)
    \tkzLabelPoints[right](Q)
\end{tikzpicture}

